Capacitive deionization of water using effective electrodes and methods of preparation thereof

Abstract

A working electrode includes an outer layer including carbonized date palm frond carbon nanoparticles having a particle size of less than 100 nanometers (nm), single-wall carbon nanotubes (SWCNTs), and a polyvinylidene fluoride binder. The working electrode further includes a graphite substrate on which the outer layer is disposed. The I D /I G ratio of the electrode measured in the Raman spectrum is 2.0 or greater.

1 : A working electrode, including:
 an outer layer including:   carbonized date palm frond carbon nanoparticles having a particle size of less than 100 nanometres (nm);   single-wall carbon nanotubes (SWCNTs);   a binder,   wherein the binder is a polyvinylidene fluoride, and   a graphite substrate on which the outer layer is disposed,   wherein the I D /I G  ratio of the electrode measured in the Raman spectrum is 2.0 or greater.   
     
     
         2 : The working electrode of  claim 1 , wherein the outer layer of the working electrode includes pores having a diameter of 20 to 2000 nm, globular clusters having the longest dimension of 500 to 5000 nm, and a network of nanowires, and wherein the working electrode has a salt adsorption capacity of at least 100 mg/g at a salt concentration of 1000 ppm and at least 400 mg/g at salt concentration of 5000 ppm. 
     
     
         3 : The working electrode of  claim 1 , wherein the carbonized date palm frond carbon nanoparticles have a Brunauer-Emmett-Teller surface area of 900 to 1500 meters square per gram (m 2 /g). 
     
     
         4 : The working electrode of  claim 1 , wherein the carbonized date palm frond carbon nanoparticles are made by a process, including:
 carbonizing the date palm fronds at a temperature of 350 to 450 degrees Celsius (° C.) for 2 to 4 hours (h);   ball milling the carbonized date palm fronds for 0.5 to 16 h at a speed of 150 to 250 revolutions per minute (rpms);   mixing the ball milled carbonized date palm fronds with a base in water to form a solution, wherein the ball milled carbonized date palm fronds and the base have a weight ratio of 1:3 to 1:5,   heating the solution at a temperature of 550 to 650° C. for 1 to 3 h to form the chemically active carbon nanoparticles of date palm fronds.   
     
     
         5 : The working electrode of  claim 1 , wherein the working electrode is made by a process, including:
 dissolving the polyvinylidene fluoride in a polar solvent;   mixing the chemically active carbon nanoparticles of date palm fronds and the SWCNTs with the polyvinylidene fluoride in the polar solvent to form a mixture;   sonicating the mixture to form a slurry;   depositing the slurry on the graphite substrate; and   drying the slurry on the graphite substrate at a temperature of 100 to 120° C. for 4 to 6 h to form the working electrode,   wherein a weight ratio of the chemically active carbon nanoparticles of date palm fronds to the SWCNTs to the polyvinylidene fluoride is from 25 to 30:0.5 to 2:1 to 3.   
     
     
         6 : A method of desalination, including:
 contacting the working electrode of  claim 1 , a reference electrode, and a counter electrode with an aqueous solution in a feed tank,   wherein the reference electrode is a silver/silver chloride (Ag/AgCl) electrode,   wherein the counter electrode is a platinum electrode,   wherein the aqueous solution includes one or more salts,   connecting the working electrode, the reference electrode, and the counter electrode to a potentiostat;   circulating the aqueous solution through the feed tank;   applying a potential to the working electrode; and   absorbing the one or more salts.   
     
     
         7 : The method of  claim 6 , wherein circulating occurs at a rate of 15 to 20 mL/minute. 
     
     
         8 : The method of  claim 6 , wherein the applied voltage is from 1.5 to 1.7 volts (V) vs. Ag/AgCl. 
     
     
         9 : The method of  claim 6 , wherein the aqueous solution has an initial concentration of the one or more salts of 1000 parts per million (ppm), and the working electrode has a salt adsorption capacity of 120 to 130 milligrams per gram (mg/g). 
     
     
         10 : The method of  claim 6 , wherein the aqueous solution has an initial concentration of the one or more salts of 1000 ppm, and the working electrode has an ion removal rate of 0.45 to 0.50 milligrams per gram per second (mg/g/s). 
     
     
         11 : The method of  claim 6 , wherein the aqueous solution has an initial concentration of the one or more salts of 1000 ppm, and the working electrode has a salt adsorption capacity of at least 80% of an initial salt adsorption capacity after 50 cycles, wherein one cycle is 900 seconds (s). 
     
     
         12 : The working electrode of  claim 1 , wherein the working electrode has a specific capacitance of 230 to 300 Farad per gram (F/g) at a scan rate of 5 millivolts per second (mV/sec). 
     
     
         13 : The working electrode of  claim 1 , wherein the working electrode has a charge transfer resistance of 5 to 7 oms (Q). 
     
     
         14 : A working electrode, including:
 an outer layer including:   a carbonized chitosan cryopolymerized material;   SWCNTs;   a linker,   wherein the linker is a glutaraldehyde, and   a graphite substrate on which the outer layer is disposed.   
     
     
         15 : The working electrode of  claim 14 , wherein the outer layer of the working electrode is three-dimensional and includes nanopores, micropores, ridges, and valleys, wherein the ridges are 200 to 700 micrometers (μm) in length and the valleys are 50 to 300 μm in width between the ridges. 
     
     
         16 : The working electrode of  claim 14 , wherein the working electrode is made by a process, including:
 dissolving the chitosan in an acidic solution;   sonicating the SWCNTs with the chitosan in the acidic solution;   mixing the glutaraldehyde with the SWCNTs and the chitosan in the acidic solution to form a mixture;   depositing the mixture on the graphite substrate;   freezing the mixture on the graphite substrate at a first temperature of −10 to −30° C. for 20 to 28 h;   freezing the mixture on the graphite substrate at a second temperature of −35 to −45° C. for 20 to 28 h; and   carbonizing the mixture on the graphite substrate at a temperature of 300 to 400° C. for 1 to 3 h to form the working electrode.   
     
     
         17 : A method of desalination, including:
 contacting the working electrode of  claim 14 , a reference electrode, and a counter electrode with an aqueous solution in a feed tank,   wherein the reference electrode is a silver/silver chloride (Ag/AgCl) electrode,   wherein the counter electrode is a platinum electrode,   wherein the aqueous solution includes one or more salts,   connecting the working electrode, the reference electrode, and the counter electrode to a potentiostat;   circulating the aqueous solution through the feed tank;   applying a potential to the working electrode; and   absorbing the one or more salts.   
     
     
         18 : The method of  claim 17 , wherein the aqueous solution has an initial concentration of the one or more salts of 1000 ppm, and the working electrode has a salt adsorption capacity of 45 to 55 mg/g. 
     
     
         19 : The method of  claim 17 , wherein the aqueous solution has an initial concentration of the one or more salts of 1000 ppm, and the working electrode has a salt adsorption capacity of at least 80% of an initial salt adsorption capacity after 50 cycles, wherein one cycle is 900 s. 
     
     
         20 : The working electrode of  claim 14 , wherein the working electrode has a specific capacitance of 130 to 140 F/g at a scan rate of 5 mV/sec.